A grand solar minimum would barely make a dent in human-caused global warming

Research has shown that a grand solar minimum would offset no more than 0.3 °C of global warming

by Dana Nuccitelli, "Climate Consensus - The 97%," The Guardian, January 19, 2014

Fortunately for us, solar activity is quite stable, and a solar minimum would only have a small effect on global temperatures. Photograph: saesnes

Recent articles in the Danish newspaper Jyllands-Posten (translation available here) and in the Irish Times both ran headlines claiming that another grand solar minimum could potentially trigger an "ice age" or "mini ice age" this century. These articles actually refer to the Little Ice Age (LIA) – a period about 500 to 150 years ago when global surface temperatures were approximately 1 °C colder than they are today. This is quite different from an ice age, which are more like 5m°C colder than today. The LIA was not actually very cold on a global scale.

So, in order to trigger another LIA, a new grand solar minimum would have to cause about 1 °C cooling, plus it would have to offset the continued human-caused global warming of 1 to 5 °C by 2100, depending on how our greenhouse gas emissions change over the next century.

In the Jyllands-Posten article, Henrik Svensmark (the main scientist behind the hypothesis that the sun has a significant indirect impact on global climate via galactic cosmic rays) was a bit more measured, suggesting,

"I can imagine that it will become 0.2 °C colder. I would be surprised if it became 1–2 °C"

So these two articles are suggesting that a grand solar minimum could have a net cooling effect in the ballpark of 1 to 6 °C, depending on how human greenhouse gas emissions change over the next century. Is it plausible that a grand solar minimum could make that happen?

The short answer is, 'No.'

Fortunately, Solar Output is Stable

We're fortunate that the amount of solar radiation reaching the Earth's surface is very stable. Climate contrarians will often ask if we'd prefer if the planet were warming or cooling, suggesting that global warming is a good thing because at least the planet isn't getting colder. This is a false dichotomy - an ideal climate is a stable one.

The relatively stable climate over the past 10,000 years has allowed establishment of human civilization, by making it possible to create large stationary agricultural farms because we could rely on stable weather patterns. During that time, net global surface temperatures changes haven't exceeded 1 °C from the coldest to the hottest climates, though we're now approaching that degree of change, with 1 °C warming since the LIA, 0.8 °C of that over the past century, with much more to come.

What difference would a grand solar minimum make in the amount of solar energy reaching Earth? Two examples are the Maunder Minimum, a period of very low solar activity between 1645 and 1715, and the Dalton Minimum, a period of low (but not as low as the Maunder Minimum) solar activity between 1790 and 1830.

400 years of sunspot observations data. Created by Robert Rohde, via Wikipedia.

Relative to current levels, the Dalton Minimum represents a 0.08% decrease in the amount of solar radiation reaching the Earth's surface, and the Maunder Minimum represents a 0.25% decline. That's how stable solar activity is. That's also why we're playing with fire by increasing the greenhouse effect so much and so quickly. We're threatening the stability of the climate that has been so favorable to our development.

Peer-Reviewed Research Says Global Warming will Continue

There have been several studies in recent years investigating what impact another grand solar minimum would have on global surface temperatures, since solar research suggests it's possible we could be due for another extended solar minimum. Generally these studies will run climate model simulations under a given greenhouse gas emissions scenario with stable solar activity, then run the same scenario with the sun going into a grand minimum, and look at the difference in resulting global surface temperature changes.

Using this approach, Feulner and Rahmstorf (2010) (PDF available here) estimated that another solar minimum equivalent to the Dalton and Maunder Minima would cause 0.09 °C and 0.26 °C cooling, respectively.

The global mean temperature difference is shown for the time period 1900 to 2100 for the IPCC A2 emissions scenario. The red line shows predicted temperature change for the current level of solar activity, the blue line shows predicted temperature change for solar activity at the much lower level of the Maunder Minimum, and the black line shows observed temperatures through 2010. Adapted from Feulner & Rahmstorf (2010) by SkepticalScience.com

Jones et al. (2012) (PDF available here) arrived at a nearly identical result, with cooling from another Dalton or Maunder Minimum at 0.09 °C and 0.26 °C, respectively. Similarly, a new paper by Anet et al. (2013) found that a grand solar minimum will cause no more than 0.3 °C cooling over the 21st century.

Consistent with these previous studies, Meehl et al. (2013) (PDF available here) estimate a Maunder Minimum would cause about 0.26 °C cooling, but as soon as solar activity began to rise again, that cooling would be offset by solar warming. This is a key point, because a grand solar minimum would not be a permanent change. These solar minima last for a few decades, but eventually solar activity rises once again. Thus any cooling caused by a solar minimum would only be temporary.

The cooling effect of a grand solar minimum can also be estimated very easily without the aid of climate models, because the change in the amount of solar radiation reaching the Earth's surface is directly proportional to the temperature change it causes. Performing this calculation yields the same result as the model-based research: approximately 0.3 °C cooling from another Maunder-type grand solar minimum. Click here to see the details behind the calculation.

The Heating of the Deep Oceans

In the Jyllands-Posten article, Svensmark also disputes the data showing the accelerated accumulation of heat in the deep oceans.

"How can the ocean below 700 meters be heated up, without the upper ocean warming up accordingly?"

This is an increasingly common argument made by climate contrarians, and a bit of a strange one. The data are what they are - we've measured the deep ocean warming, including with reliable instruments on Argo buoys for close to a decade now. Even if we couldn't explain how the heat got there, it's there.

5-year averages of ocean heat content 0-700 meters (red) and 0-2000 meters (black), from the National Oceanographic Data Center

But let's address the question anyway - do we expect to have seen some obvious indication of heat being transferred from the shallow to deep ocean layers?

It's certainly not clear that we should. Consider the analogy of a bathtub. Water from the faucet represents heat entering the shallow ocean layer. Water exiting the drain represents heat leaving the shallow oceans and entering the deep oceans. The water level in the bathtub represents the heat in the shallow ocean layer (which is what we measure).

If the amount of water entering the tub from the faucet is the same as the amount of water draining out of the tub, the water level in the tub won't change. Yet the water still flows down the drain. Climate scientist Gavin Schmidt has discussed this point, summarized here.

In short, we wouldn't necessarily see the heat being transferred through the shallow to the deep oceans. However, there has been plenty of warming of the shallow oceans that could have been transferred to the deeper oceans. In our case, the water is flowing into the tub faster than it's draining out - the shallow oceans are warming fast, as the figure above illustrates.

Svensmark Gets Ocean Warming Wrong

Unfortunately Svensmark appears to be unfamiliar with this ocean heating data, saying,

"The thousands of buoys that we have deployed after 2003 to measure the ocean temperature, have not registered any temperature rise."

This is just totally wrong, even if we ignore the rapid warming of the deep oceans (as is clear from a simple examination of the figure above). The ocean heat content data can be downloaded from the National Oceanographic Data Center here. The heating trend since 2003 in the upper 700 meters of oceans is equivalent to nearly 1 Hiroshima atomic bomb detonation per second (plus another 3 per second in the deep oceans). Both the shallow and deep oceans are accumulating a whole lot of heat, with no signs of slowing whatsoever. If anything, the heating of the oceans and the planet as a whole is accelerating.

Human Influence on Climate Change is Bigger than the Sun's

The bottom line is that the sun and the amount of solar radiation reaching Earth are very stable. Even during the Maunder and Dalton grand solar minima, global cooling was relatively small - smaller than the amount of global warming caused by human greenhouse gas emissions over the past century.

A new grand solar minimum would not trigger another LIA; in fact, the maximum 0.3°C cooling would barely make a dent in the human-caused global warming over the next century. While it would be enough to offset to about a decade's worth of human-caused warming, it's also important to bear in mind that any solar cooling would only be temporary, until the end of the solar minimum.

The science is quite clear that the human influence on climate change has become bigger than the sun's. At this point, speculation about another mini ice age is pure fantasy.

http://www.theguardian.com/environment/climate-consensus-97-per-cent/2013/aug/14/global-warming-solar-minimum-barely-dent

Peter Sinclair: Myth of the Mini Ice Age [Climate Denial Crock of the Week]

Climate Denial Crock of the Week by Peter Sinclair:  Myth of the Mini Ice Age

http://www.youtube.com/watch?v=IQHqgdvXTxE

What if the Sun went into a new Grand Minimum? Guest commentary by Georg Feulner, Real Climate, June 19, 2011

What if the Sun went into a new Grand Minimum?

Guest commentary by Georg Feulner, Real Climate, June 19, 2011

During a meeting of the Solar Physics Division of the American Astronomical Society, solar physicists have just announced a prediction that the Sun might enter an extended period of low activity (a ‘grand minimum’) similar to the Maunder Minimum in the 17th century. In this post I will explore the background of this announcement and discuss implications for Earth’s climate.

It has been known for a long time that solar activity shows a very regular pattern. Every 11 years the Sun is particularly active, and numerous dark sunspots are visible on its surface. These maxima of solar activity are separated by times of low activity when only few (if any) sunspots appear.

Figure 1: The Sun in visible light during an activity maximum (left) and during the last (and rather extraordinary) 11-year minimum during which it appeared spotless most of the time. Source: NASA Earth Observatory/SOHO.

One could think that the Sun emits less light during a solar maximum because of the many dark spots. In fact it is the other way round, since active regions around the sunspots emit more radiation than is “lost” in the cooler sunspot areas. This effect can be best seen in ultraviolet images of the Sun.

Figure 2: The Sun in ultraviolet light during a maximum (left) and a minimum (right). Source: NASA Earth Observatory/SOHO.

An analysis of historic sunspot observations shows that the 11-year solar activity cycle was interrupted during the late 17th century.

This period of time, during which the Sun appeared without sunspots most of the time, was called the Maunder Minimum by Jack Eddy in his famous Science paper. (Alliteratively named after Edward Maunder, although it was actually first discovered by Gustav Spörer.)

Figure 3: Observations of the number of sunspots over the last four centuries. Source: Wikimedia Commons/Global Warming Art.

The Maunder Minimum falls within the climatically cooler period of the “Little Ice Age,” during which temperatures were particularly low over continents in the Northern hemisphere (especially in winter). It has long been suspected that the low solar activity during the Maunder Minimum was one of the causes of the Little Ice Age, although other factors like a small drop in greenhouse gas concentrations around 1600 and strong volcanic eruptions during that time likely played a role as well.

Solar physicists do not yet understand how an extended solar-activity low like the Maunder Minimum arises. Yet there is recent observational evidence for an unusual behavior of the Sun during the current cycle 24, including a missing zonal wind flow within the Sun, decreasing magnetic field strength of sunspots and lower activity around the poles of the Sun. 

These observations prompted Frank Hill and colleagues to suggest that the Sun might enter a new Maunder-like minimum after the current 11-year cycle ends (i.e., after 2020 or so).

It remains to be seen whether this prognosis turns out to be true (there have been some doubts expressed), but since grand minima of solar activity did occur in the past, it is certainly interesting to explore what effects such a minimum might have on 21st century climate if it did occur. This is precisely the question Stefan Rahmstorf and I investigated in a study published last year (see also our press release. (Earlier estimates for the size of this effect can be found here and here.) In our study we find that a new Maunder Minimum would lead to a cooling of 0.3 °C in the year 2100 at most – relative to an expected anthropogenic warming of around 4 °C. (The amount of warming in the 21st century depends on assumptions about future emissions, of course).

Figure 4: Rise of global temperature (relative to 1961-1990) until the year 2100 for two different emission scenarios (A1B, red; A2, magenta). The dashed lines show the slightly reduced warming in case a Maunder-like solar minimum should occur during the 21st century. Source: PIK.

According to these results, a 21st-century Maunder Minimum would only slightly diminish future warming. Moreover, it would be only a temporary effect since all known grand solar minima have only lasted for a few decades. Critics of this result might argue that the solar forcing in these experiments is only based on the estimated change in total irradiance, which might be an underestimate, or that does not include potential indirect amplifying effects (via an ozone response to UV changes, or galactic cosmic rays affecting clouds). However, our model reproduces the historic Maunder minimum with these estimates of solar irradiance. 

Furthermore, even if one multiplied the solar effects by a huge factor of 5 (which is unrealistic), no absolute cooling would take place (the temperatures would be temporarily cooler than the base scenario, but the trends would still be warming).

It is clear that if a grand minimum were to happen it would be a tremendously exciting opportunity for solar physicists, however it is unlikely to be very exciting for anyone else.

Update 23 June: Here is a nice tongue-in-cheek video on the media response to this story.

http://www.realclimate.org/index.php/archives/2011/06/what-if-the-sun-went-into-a-new-grand-minimum/#more-7928

Sunspot Drop Won’t Cause Global Cooling

• By Brandon Keim , Wired 
• 
 
• June 15, 2011

News that solar activity might fizzle for a few decades has prompted talk of a new “Little Ice Age,” even a quick fix for global warming. But that’s just not going to happen.

The cooling impact of the last prolonged solar lull “was probably only a couple tenths of a degree Celsius,” said climatologist Michael Mann of Penn State University. “It’s a tiny blip on the radar screen if you’re looking at the driving factors behind climate change.”

The possibility of imminent solar dormancy was raised by reports from the ongoing American Astronomical Society meeting of fading sunspots and dips in the sun’s magnetic patterns. Those are considered portents of solar inactivity, suggesting that the next solar minimum — a natural downturn in activity — would be especially pronounced, perhaps lasting for decades.

The frozen Thames, circa 1677. Artist unknown, Wikimedia Commons.

When that last happened, between the mid-17th and early 18th centuries, northern Europe experienced a period of unusually cold weather. Known as theMaunder Minimum, or more conversationally as the Little Ice Age, it’s a period historicized by accounts of ice skating on the Thames and seasonal inns built on Baltic Sea ice.

Press accounts of the new solar reports played up the Maunder Minimum angle, hinting that it might happen again. Some even implied that global warming might be counteracted.

In fact, the meaning of the latest sunspot reports is still being debated, as Andrew Revkin at Dot Earth has chronicled. But even if they really do portend a decades-long solar lull, studies already point to a minimal effect on climate.

Most Little Ice Age cooling appears to have been the result of coincidentally high volcanic activity that cloaked Earth in sunlight-blocking soot. As for the sun, a study published in 2001 in Science found that reduced solar activity produced a cooling effect of about 0.5 °F. In other estimates, the cooling is even more insignificant.

‘Global mean temperatures in the year 2100 would most likely be diminished by about 0.1°C.’

More recently, in a 2010 Geophysical Research Letters study, Georg Fuelner and Stefan Rahmstorf of the Potsdam Institute for Climate Impact Research asked the question directly: What would happen if Earth experienced another 70-year-long solar minimum?

The answer can be seen in the image at the top of this post, which estimates the temperature difference between a solar minimum future under “middle-of-the-road” climate scenarios and the Maunder Minimum. In a nutshell: It’s going to be much, much hotter in the future, solar minimum or not.

“Global mean temperatures in the year 2100 would most likely be diminished by about 0.1 °C,” wrote Rahmstorf and Fuelner. And even if their models and assumptions were so uncertain as to be off by a factor of three, that still puts the cooling at just 0.3 °C, or about 0.5 °F.

Compared to the end-of-century global average temperature increase predicted by the Intergovernmental Panel on Climate Change — about 5 °F under mid-range scenarios, and 7 °F under more realistic scenarios — solar cooling would be negligible.

“A new Maunder‐type solar activity minimum cannot offset the global warming caused by human greenhouse gas emissions,” concluded Rahmstorf and Fuelner.

“The example I like to use is that greenhouse warming right now is the equivalent of 2 watts of power illuminating every square meter of the Earth’s surface. It’s like a Christmas tree light over every square meter. By mid-century, it will be closer to 4 watts,” said Mann, who was a co-author on that 2001 Science paper. “The maximum impact factor of the sun is 0.2 watts per meter squared.”

At most, a prolonged solar minimum would temporarily offset rising global temperatures for a few years, perhaps a couple decades, said NASA climatologist David Rind, who has also studied Maunder Minimum dynamics. But “when the sunspots return, the additional energy will cause additional warming,” he said.

“To point to this as something that could in any way ameliorate greenhouse gas warming is folly,” said Mann.

Image: Average global temperature differences, 2071-2100 and 1681-1710, assuming another period of Maunder Minimum-like solar inactivity. (Feulner & Rahmstorf, Geophysical Research Letters).

http://www.wired.com/wiredscience/2011/06/solar-minimum-climate/

National Solar Observatory Press Release; "What's Down with the Sun? Major Drop in Solar Activity Predicted"; Dr. Frank Hill says "We are NOT predicting a mini-ice age..."

National Solar Observatory What's Down with the Sun? Major Drop in Solar Activity Predicted [Dr. Frank Hill: "We are NOT predicting a mini-ice age."]

---

THE FOLLOWING RELEASE WAS RECEIVED JOINTLY FROM THE NATIONAL SOLAR OBSERVATORY IN SUNSPOT, NEW MEXICO, AND THE SOLAR PHYSICS DIVISION OF THE AMERICAN ASTRONOMICAL SOCIETY AND IS FORWARDED FOR YOUR INFORMATION (FORWARDING DOES NOT IMPLY ENDORSEMENT BY THE AMERICAN ASTRONOMICAL SOCIETY). Rick Fienberg, AAS Press Officer: rick.fienberg@aas.org, +1 202-328-2010 x116.** This release was previously distributed to journalists under an embargo that has since expired. {RTF} **
June 14, 2011
Contacts:
Dave Dooling
NSO Education and Public Outreach
+1 575-434-7015 (office); +1 575-921-8736 (cell)
dooling@nso.edu
Craig DeForest
AAS/SPD Press Officer
+1 303-641-5679 (cell)
deforest@boulder.swri.edu
Text & Images: http://www.boulder.swri.edu/~deforest/SPD-sunspot-release

WHAT'S DOWN WITH THE SUN?
MAJOR DROP IN SOLAR ACTIVITY PREDICTED

A missing jet stream, fading spots, and slower activity near the poles say that our Sun is heading for a rest period even as it is acting up for the first time in years, according to scientists at the National Solar Observatory (NSO) and the Air Force Research Laboratory (AFRL).


As the current sunspot cycle, Cycle 24, begins to ramp up toward maximum, independent studies of the solar interior, visible surface, and the corona indicate that the next 11-year solar sunspot cycle, Cycle 25, will be greatly reduced or may not happen at all.


The results were announced at the annual meeting of the Solar Physics Division of the American Astronomical Society, which is being held this week at New Mexico State University in Las Cruces: http://astronomy.nmsu.edu/SPD2011/

"This is highly unusual and unexpected," Dr. Frank Hill, associate director of the NSO's Solar Synoptic Network, said of the results. "But the fact that three completely different views of the Sun point in the same direction is a powerful indicator that the sunspot cycle may be going into hibernation."


Spot numbers and other solar activity rise and fall about every 11 years, which is half of the Sun's 22-year magnetic interval since the Sun's magnetic poles reverse with each cycle. An immediate question is whether this slowdown presages a second Maunder Minimum, a 70-year period with virtually no sunspots during 1645-1715.


Hill is the lead author on one of three papers on these results being presented this week. Using data from the Global Oscillation Network Group (GONG) of six observing stations around the world, the team translates surface pulsations caused by sound reverberating through the Sun into models of the internal structure. One of their discoveries is an east-west zonal wind flow inside the Sun, called the torsional oscillation, which starts at mid-latitudes and migrates towards the equator. The latitude of this wind stream matches the new spot formation in each cycle, and successfully predicted the late onset of the current Cycle 24.
"We expected to see the start of the zonal flow for Cycle 25 by now," Hill explained, "but we see no sign of it. This indicates that the start of Cycle 25 may be delayed to 2021 or 2022, or may not happen at all."


In the second paper, Matt Penn and William Livingston see a long-term weakening trend in the strength of sunspots, and predict that by Cycle 25 magnetic fields erupting on the Sun will be so weak that few if any sunspots will be formed. Spots are formed when intense magnetic flux tubes erupt from the interior and keep cooled gas from circulating back to the interior. For typical sunspots this magnetism has a strength of 2,500 to 3,500 gauss (Earth's magnetic field is less than 1 gauss at the surface); the field must reach at least 1,500 gauss to form a dark spot.


Using more than 13 years of sunspot data collected at the McMath-Pierce Telescope at Kitt Peak in Arizona, Penn and Livingston observed that the average field strength declined about 50 gauss per year during Cycle 23 and now in Cycle 24. They also observed that spot temperatures have risen exactly as expected for such changes in the magnetic field. If the trend continues, the field strength will drop below the 1,500 gauss threshold and spots will largely disappear as the magnetic field is no longer strong enough to overcome convective forces on the solar surface.


Moving outward, Richard Altrock, manager of the Air Force's coronal research program at NSO's Sunspot, NM, facilities has observed a slowing of the "rush to the poles," the rapid poleward march of magnetic activity observed in the Sun's faint corona. Altrock used four decades of observations with NSO's 40-cm (16-inch) coronagraphic telescope at Sunspot.
"A key thing to understand is that those wonderful, delicate coronal features are actually powerful, robust magnetic structures rooted in the interior of the Sun," Altrock explained. "Changes we see in the corona reflect changes deep inside the Sun."


Altrock used a photometer to map iron heated to 2 million °C (3.6 million °F). Stripped of half of its electrons, it is easily concentrated by magnetism rising from the Sun. In a well-known pattern, new solar activity emerges first at about 70 degrees latitude at the start of a cycle, then towards the equator as the cycle ages. At the same time, the new magnetic fields push remnants of the older cycle as far as 85 degrees poleward.


"In cycles 21 through 23, solar maximum occurred when this rush appeared at an average latitude of 76 degrees," Altrock said. "Cycle 24 started out late and slow and may not be strong enough to create a rush to the poles, indicating we'll see a very weak solar maximum in 2013, if at all. If the rush to the poles fails to complete, this creates a tremendous dilemma for the theorists, as it would mean that Cycle 23's magnetic field will not completely disappear from the polar regions (the rush to the poles accomplishes this feat). No one knows what the Sun will do in that case."


All three of these lines of research to point to the familiar sunspot cycle shutting down for a while.


"If we are right," Hill concluded, "this could be the last solar maximum we'll see for a few decades. That would affect everything from space exploration to Earth's climate."


In response to news inquiries and stories, Dr. Frank Hill issued a follow-up statement:


"We are NOT predicting a mini-ice age. We are predicting the behavior of the solar cycle. In my opinion, it is a huge leap from that to an abrupt global cooling, since the connections between solar activity and climate are still very poorly understood. My understanding is that current calculations suggest only a 0.3 °C decrease from a Maunder-like minimum, too small for an ice age. It is unfortunate that the global warming/cooling studies have become so politically polarizing."


# # # These results have been presented at the current meeting of the AAS/SPD.
Citations:
16.10: "Large-Scale Zonal Flows During the Solar Minimum -- Where Is Cycle 25?" by Frank Hill, R. Howe, R. Komm, J. Christensen-Dalsgaard, T.P. Larson, J. Schou & M. J. Thompson.
17.21: "A Decade of Diminishing Sunspot Vigor" by W. C. Livingston, M. Penn & L. Svalgard.
18.04: "Whither Goes Cycle 24? A View from the Fe XIV Corona" by R. C. Altrock.


http://www2.nso.edu/press/SolarActivityDrop.html

Peter Sinclair: What if the Sun Goes into another Maunder Minimum?

Graph of the Day: What if the Sun Goes into another Maunder Minimum?

by Peter Sinclair, June 16, 2011

By now, you’ve probably heard the news. The sun is going cold, and all that talk about global warming was just a fad, just like Glenn Beck always said. And by the way, scientists say we’re going into a new ice age. It’s a climate crock I’ve treated before.

Now, Fox News and others are spinning reports about recent model predictions of low solar activity.

What do the actual scientists who did the work say? 

Something considerably less dramatic, according to Reuters:

“...contrary to some media reports, this does not mean a new Ice Age is coming, Frank Hill of the National Solar Observatory said in a telephone interview. 

“We have not predicted a Little Ice Age,” Hill said, speaking from an astronomical meeting in New Mexico. “We have predicted something going on with the Sun.”

International Business Times:

Scientists are in no doubt that the sun has been acting oddly in recent years. Sunspot numbers ebb and flow in cycles lasting around 11 years but over the past three years, observable sunspots have been mostly missing. 

These spots have been used by scientists to indicate the sun’s magnetic activity is diminishing, and that the sun may even be shrinking. Since 2007, visible sunspot activity has stalled, leading researchers to suggest that the next solar maximum (due in 2013) could be a long while coming. Instead, the sun could go into a prolonged lull lasting several decades.

New Scientist observes:

Ordinarily, its activity varies over about 11 years, but since 2007 it seems to have stalled. 

This week a string of researchers presented new data showing that the sun still isn’t perking up. That means, rather than having a solar maximum in 2013, we might not see one for a long time. Instead, the sun could go into a prolonged lull lasting several decades. 

This has happened before, the most famous example being the Maunder Minimum of 1645-1715 when the sun became less luminous than normal and hardly any sunspots were seen on its surface. There is plenty of evidence that such “grand minima” cool the Earth: it’s one of the more dramatic effects the sun’s changing activity can have on our climate. The Maunder Minimum itself is widely linked to the Little Ice Age. 

Here’s where the story lurches away from reality. According to the Global Warming Policy Foundation (of whom more here), the sun’s shutdown means that
The Earth – far from facing a global warming problem – is actually headed into a mini ice age. 

There’s a simple problem with this claim. Let’s assume that grand minima really do cool Earth’s climate: not every climate scientist is convinced of that, but for the sake of argument let’s go with it. Now the question becomes: how much do they cool it, and for how long? 

The straightforward answer is: not enough. Last year researchers modelled what would happen to global temperatures if a grand minimum started now and continued until 2100. They found that it would lower temperatures by 0.3 °C at most.

Scientists have been studying and remarking on  the sun’s peculiar behavior for years, and as long ago as 2009, NASA scientists wrote:

Solar irradiance: The solar output remains low (Fig. 4), at the lowest level in the period since satellite measurements began in the late 1970s, and the time since the prior solar minimum is already 12 years, two years longer than the prior two cycles. This has led some people to speculate that we may be entering a “Maunder Minimum” situation, a period of reduced irradiance that could last for decades. Most solar physicists expect the irradiance to begin to pick up in the next several months — there are indications, from the polarity of the few recent sunspots, that the new cycle is beginning. 

 

However, let’s assume that the solar irradiance does not recover. In that case, the negative forcing, relative to the mean solar irradiance is equivalent to seven years of CO₂ increase at current growth rates. So do not look for a new “Little Ice Age” in any case.

NASA’s take was born out, as, even in the midst of the lowest solar minimum in a century, 2009, and 2010, were, respectively, the number 2, and number one warmest years in NASA’s instrumental record globally.

Wired has this take:

The possibility of imminent solar dormancy was raised by reports from the ongoing American Astronomical Society meeting of fading sunspots and dips in the sun’s magnetic patterns. Those are considered portents of solar inactivity, suggesting that the next solar minimum — a natural downturn in activity — would be especially pronounced, perhaps lasting for decades.
When that last happened, between the mid-17th and early 18th centuries, northern Europe experienced a period of unusually cold weather. Known as theMaunder Minimum, or more conversationally as the Little Ice Age, it’s a period historicized by accounts of ice skating on the Thames and seasonal inns built on Baltic Sea ice. 

Press accounts of the new solar reports played up the Maunder Minimum angle, hinting that it might happen again. Some even implied that global warming might be counteracted. 

In fact, the meaning of the latest sunspot reports is still being debated, as Andrew Revkin at Dot Earth has chronicled. But even if they really do portend a decades-long solar lull, studies already point to a minimal effect on climate. 

Most Little Ice Age cooling appears to have been the result of coincidentally high volcanic activity that cloaked Earth in sunlight-blocking soot. As for the sun, a study published in 2001 in Science found that reduced solar activity produced a cooling effect of about 0.5 degrees Fahrenheit. In other estimates, the cooling is even more insignificant.

The Wired piece quotes Mike Mann of Penn State, comparing the sun’s fluctuations to greenhouse warming.

“The example I like to use is that greenhouse warming right now is the equivalent of 2 watts of power illuminating every square meter of the Earth’s surface. It’s like a Christmas tree light over every square meter. By mid-century, it will be closer to 4 watts,….the maximum impact factor of the sun is 0.2 watts per meter squared.”

A recent paper by Georg Fulner and Stefan Rahmstorf asked what might happen to earth’s climate in the event of a new solar minimum. That paper’s key graph is adapted above. The paper’s conclusion:

In summary, global mean temperatures in the year 2100 would most likely be diminished by about 0.1°C. Even taking into account all uncertainties in the temperature re- construction, the forcings, and the model physics, the overall uncertainty is estimated to be at most a factor of 3, so the offset should not be larger than 0.3°C. Comparing this to the 3.7°C and 4.5°C temperature rise relative to 1961–1990 until the end of the century under the IPCC A1B and A2 emission scenarios, respectively, a new Maunder‐type solar activity minimum cannot offset the global warming caused by human greenhouse gas emissions.

http://climatecrocks.com/2011/06/16/graph-of-the-day-what-if-the-sun-goes-into-another-maunder-minimum/ 

Seth Borenstein, AP Science Writer: "Goodnight sun: Sunspots may disappear for years"

Goodnight sun: Sunspots may disappear for years

by SETH BORENSTEIN, AP Science Writer, June 14, 2011

WASHINGTON – The sun is heading into an unusual and extended hibernation, scientists predict. Around 2020, sunspots may disappear for years, maybe decades.

But scientists say it is nothing to worry about. Solar storm activity has little to do with life-giving light and warmth from the sun. The effects from a calmer sun are mostly good. There'd be fewer disruptions of satellites and power systems. And it might mean a little less increase in global warming.

It's happened before, but not for a couple centuries.

"The solar cycle is maybe going into hiatus, sort of like a summertime TV show," said National Solar Observatory associate director Frank Hill, the lead author of a scientific presentation at a solar physics conference in New Mexico.

Scientists don't know why the sun is going quiet. But all the signs are there.

Hill and colleagues based their prediction on three changes in the sun spotted by scientific teams: Weakening sunspots, fewer streams spewing from the poles of the sun's corona and a disappearing solar jet stream.

Those three cues show, "there's a good possibility that the sun could be going into some sort of state from which it takes a long time to recover," said Richard Altrock, an astrophysicist at the Air Force Research Laboratory and study co-author.

The prediction is specifically aimed at the solar cycle starting in 2020. Experts say the sun has already been unusually quiet for about four years with few sunspots — higher magnetic areas that appear as dark spots.

The enormous magnetic field of the sun dictates the solar cycle, which includes sunspots, solar wind and ejection of fast-moving particles that sometimes hit Earth. Every 22 years, the sun's magnetic field switches north and south, creating an 11-year sunspot cycle. At peak times, like 2001, there are sunspots every day and more frequent solar flares and storms that could disrupt satellites.

Earlier this month, David Hathaway, NASA's top solar storm scientist, predicted that the current cycle, which started around 2009, will be the weakest in a century. Hathaway is not part of Tuesday's prediction.

Altrock also thinks the current cycle won't have much solar activity. He tracks streamers from the solar corona, the sun's outer atmosphere seen during eclipses. The streamers normally get busy around the sun's poles a few years before peak solar storm activity. That "rush to the poles" would have happened by now, but it hasn't and there's no sign of it yet. That also means the cycle after that is uncertain, he said.

Matt Penn of the National Solar Observatory, another study co-author, said sunspot magnetic fields have been steadily decreasing in strength since 1998. If they continue on the current pace, their magnetic fields will be too weak to become spots as of 2022 or so, he said.

Jet streams on the sun's surface and below are also early indicators of solar storm activity, and they haven't formed yet for the 2020 cycle. That indicates that there will be little or delayed activity in that cycle, said Hill, who tracks jet streams.

"People shouldn't be scared of this," said David McComas, a scientist at the Southwest Research Institute in San Antonio, who wasn't part of the team. "This is about the magnetic field and the ionized gas coming out of the sun. It's a reduction in that, not the light and the heat."

There are questions about what this means for Earth's climate. Three times in the past the regular 11-year solar cycle has gone on an extended vacation — at the same time as cool periods on Earth.

Skeptics of man-made global warming from the burning of fossil fuels have often pointed to solar radiation as a possible cause of a warming Earth, but they are in the minority among scientists. The Earth has warmed as solar activity has decreased.

Andrew Weaver, a climate scientist at the University of Victoria, said there could be small temperature effects, but they are far weaker than the strength of man-made global warming from carbon dioxide and methane. He noted that in 2010, when solar activity was mostly absent, Earth tied for its hottest year in more than a century of record-keeping.

Hill and colleagues wouldn't discuss the effects of a quiet sun on temperature or global warming. 

"If our predictions are true, we'll have a wonderful experiment that will determine whether the sun has any effect on global warming," Hill said.

http://news.yahoo.com/s/ap/20110614/ap_on_sc/us_sci_quiet_sun